Conventionally, an epoxy resin composition using an acid anhydride-based hardening agent provides a transparent hardened material and has been suitably used as a sealing material for light-emitting devices having high heat resistance, such as light-emitting diodes and photodiodes. However, with recent development of high-performance optical semiconductors, a hardened material, which has not only good transparency and high heat resistance but also excellent light resistance, oxidation resistance and crack resistance at the time of a hot and cold cycle in accordance with the on/off cycle of an LED, has been required as a sealing resin. Conventional compositions containing an epoxy resin, such as bisphenol A-based epoxy resin and bisphenol F-based epoxy resin, as a main component, actually do not have sufficient properties.
Epoxy silicone having a siloxane skeleton as a repeat unit and an epoxy group as an organic group has an excellent transparency and heat resistance, which is provided by an epoxy resin, and additionally, light resistance and oxidation resistance, which is provided by silicone. In addition to these, it is further expected that epoxy silicone may have flexibility. For the reason, epoxy silicone has drawn attention as a high-performance sealing material.
For example, Patent Document 1 proposes epoxy silicone, which has a T structure as an essential repeat unit and an epoxy group-containing organic group within the range of 0.1 to 40 mol % based on whole organic groups binding to a silicon atom in a molecule. However, the epoxy silicone formed of a T structure as a main component is brittle and therefore, it is difficult to satisfy crack resistance required for a light-emitting device sealing material.
Patent Document 2 discloses epoxy siloxane formed of a reaction product of vinyl silicone, hydrogenated silyl functional silicone and an olefin epoxy compound. Furthermore, Patent Document 3 discloses an epoxy group-containing organopolysiloxane formed of a reaction product of an organopolysiloxane having a hydroxyl group at both ends, an organohydropolysiloxane, and an epoxy group and alkenyl group-containing compound. These polysiloxanes are used as an ultraviolet curable mix composition for strippable paint. However, these specifications describe nothing about optical uses thereof such as optical semiconductors.
Patent Documents 4 and 5 describe an organohydrogensiloxane compound, which is obtained by hydrosilanizing 5 to 50% of the SiH bonds of an organohydrogensilicone compound (which is obtained by the reaction between organohydrogencyclosiloxane and organopolysiloxane having an unsaturated aliphatic group) with allyl-glycidyl ether or vinylcyclohexene epoxide, and the use thereof in hardened coating. The characteristics of the organohydrogensiloxane compound reside in that the SiH units are partly hydrosilylated with an epoxy compound and part of the SiH units remains unreacted. The SiH units unreacted are used further in a crosslinking reaction as release-coating materials, and the like. However, these specifications describe nothing about application to optical uses thereof such as optical semiconductors.
Patent Document 6 discloses a telechelic siloxane polymer having a plurality of epoxy groups at an end. This polymer is obtained by the reaction of a polyorganosiloxane having a vinyl group at an end, and an organosiloxane oligomer having at least one SiH unit with an excessive amount of alkenyl group-containing epoxy compound. The specification describes use of this polymer as a release-coating material but nothing about application to optical uses thereof such as optical semiconductors.
Patent Document 7 describes a composition containing a silicone compound having a molecular weight within a specific range and having at least two epoxy groups within a molecule, and use of the composition in an optical semiconductor sealing material. However, the resin composition is insufficient in light resistance. The crack resistance and adhesiveness thereof do not reach satisfactory levels.
In addition, the above Patent Documents 2 to 7 disclose an epoxy silicone structure having a ring structure formed of a siloxane unit, and an epoxy unit in a molecule; however, disclose nothing about a bicyclo structure. The physical properties thereof are neither disclosed nor suggested.    Patent Document 1: Japanese Patent No. 3263177    Patent Document 2: Japanese Patent Laid-Open No. 7-216308    Patent Document 3: Japanese Patent Laid-Open No. 10-182826    Patent Document 4: National Publication of International Patent Application No. 2005-523980    Patent Document 5: National Publication of International Patent Application No. 2005-529989    Patent Document 6: U.S. Pat. No. 6,313,255    Patent Document 7: Japanese Patent Laid-Open No. 2005-171021